Tantalum sputtering target and method of fabrication

ABSTRACT

A process is described for processing metal which includes clock rolling a metal plate until the desired thickness is achieved to form a rolled plate. Sputtering targets and other metal articles are further described.

BACKGROUND OF THE INVENTION

The present invention relates to sputtering targets, such as tantalumand tantalum alloy-sputtering targets, and methods to make the same.

In the sputter application field, a sputtering target assembly typicallyincludes a sputter target and a backing plate. For instance, a metaltarget or metal target blank (e.g., tantalum, titanium, aluminum,copper, cobalt, tungsten, hafnium, and the like) is bonded onto abacking plate. The backing plate can be, for example, a backing plateflange assembly such as copper, aluminum, or alloys thereof. Among thefactors that can affect sputtering performance of a given sputteringtarget assembly is the grain size and crystallographic orientation ofthe grains relative to the sputtering plane. The desired grain size andcrystallographic texture are simultaneously achieved by using acombination of mechanical deformation and annealing.

Previous methods for forming the desired metallurgical structure intantalum, for instance, has included mechanical deformation by forging,rolling, extrusion, and combinations thereof. Previous methods offorming tantalum sputtering targets relied upon multiple annealing stepsbetween the mechanical deformation steps to recrystallize the grains toproduce a uniform fine grain microstructure with either the (111) or(100) crystallographic planes parallel to the sputtering target plane.

For example, Michaluk et al., U.S. Pat. No. 6,348,113, describes variousembodiments where, in one embodiment, tantalum metal is cross-rolled at90 degrees and rectangular plate is used to make circular sputteringtarget disks by cutting.

Segal (U.S. Published Patent Application No. US 2002/0153071A1) relatesto fabrication methods for FCC metals. Jepson (U.S. Published PatentApplication No. 2002/0112789 A1), Hormann et al. (U.S. Pat. No.4,884,746), Turner (U.S. Published Patent Application No. 2002/0125128A1), Zhang (U.S. Pat. No. 6,193,821), and Broussoux et al. (U.S. Pat.No. 5,615,465) relate to the production of tantalum plate for sputteringtargets and other uses by creating rectangular plates by various methodsand then cutting a circular disk from the plate. This method can be verywasteful of expensive tantalum material.

Koenigsmann et al. (U.S. Published Patent Application No. 2003/0089429)relates to the production of tantalum sputtering targets by a powdermetallurgical process. Shah et al. (U.S. Published Patent ApplicationNo. 2002/0063056 A1) relates to the production of tantalum sputteringtarget plate with strong (100) texture using lubricated dies and rollingin orthogonal directions. Segal (U.S. Pat. No. 6,238,494 B1) and Shah etal. (U.S. Pat. No. 6,348,139 B1) relate to the production of tantalumcircular plate with strong (100) texture. In this process, circulartantalum plates are produced by a combination of forging the ingot androlling. They reported that they needed to lubricate the dies duringforging and use the lowest possible temperature for recrystallization toproduce tantalum targets with strong (100) texture and suitable grainsize and crystallographic texture uniformity.

In all of these methods the tantalum deformation steps are interruptedby annealing steps in order to recrystallize the tantalum to reduce theplastic strain in the metal to avoid cracking and to remove the workhardening of the metal to make the metal easier to work.

In addition, all of these methods show the transformation of thecylindrical ingot into a rectangular or square shape by forging androlling operations and then cutting the rectangular or square plate intocircles to manufacture a circular sputtering target. This conversionfrom circular ingot shape to rectangular shape and back to circularshape is very inefficient and wasteful of material.

SUMMARY OF THE PRESENT INVENTION

It is therefore a feature of the present invention to provide a processof making metal articles, such as sputtering targets, which aresubjected to thermal-mechanical working and preferably annealed onlyonce at the end of the working process or twice with an intermediateanneal in the middle of the metal working process and an anneal at theend of the metal working process.

Another feature of the present invention is to provide a process whichforms a circular article, such as a sputtering target, while maintainingthe circular shape throughout the entire formation process.

A further feature of the present invention is to provide a metalarticle, such as a sputtering target, which has very strongcrystallographic texture, such as strong (111) crystallographic texture.

Additional features and advantages of the present invention will be setforth in part in the description that follows, and in part will beapparent from the description, or may be learned by practice of thepresent invention. The objectives and other advantages of the presentinvention will be realized and attained by means of the elements andcombinations particularly pointed out in the description and appendedclaims.

To achieve these and other advantages, and in accordance with thepurposes of the present invention, as embodied and broadly describedherein, the present invention relates to a process for processing metalwhich comprises clock rolling a metal plate with at least two rollingpasses until the desired thickness of the metal plate is achieved toform a rolled plate. Preferably, the metal is a BCC metal and, morepreferably, tantalum or niobium or alloys thereof.

The present invention further relates to a method of making a circularmetal article and comprises processing a metal ingot having acylindrical shape so that the cylindrical shape is maintained throughoutthe process.

The processes of the present invention are especially useful in formingsputtering targets.

Also, the present invention relates to metal, such as tantalum metal orniobium metal, formed from one or more of the processes of the presentinvention.

In addition, the present invention relates to sputtering targets, suchas tantalum or niobium sputtering targets, formed by imparting a truestrain, prior to annealing, of about 3.0 or higher.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of the application, illustrate some of the embodiments of thepresent invention, and together with the description, serve to explainthe principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the process steps used to fabricatemetal plate for use in manufacturing sputtering targets.

FIG. 2 is a schematic diagram showing the relationship between rollingpasses for 120-degree clock rolling.

FIG. 3 provides (111), (110) and (100) pole figures for the tantalumplate fabricated using the method shown in FIG. 1.

FIG. 4 is an electron backscatter diffraction (EBSD) map of a tantalumplate fabricated using the method shown in FIG. 1.

FIG. 5 is a table showing the true strains for various tantalum platesfabricated using a process of the present invention.

FIG. 6 is a table showing the improvement in material yield associatedwith using circular processing of ingot rather than rectangularprocessing methods.

FIG. 7 is a graph showing the reduction in earring in tantalum plateformed into cup or dome shape for use in manufacturing hollow-cathodesputtering targets when isotropic tantalum plate is produced usingcircular processing.

FIG. 8 shows a comparison of ultrasonic banding measurements on twotantalum plates; one rolled using clock rolling and the other rolledusing an orthogonal rolling process. A dramatic reduction in texturebanding is observed with clock rolling.

FIG. 9 provides (111), (110), and (100) pole figures for tantalum plateobtained by conventional orthogonal rolling.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to processes to form metal articles, suchas sputtering targets. In general, the present invention relates to theuse of clock rolling of the metal to achieve the desired dimensions ofthe rolled metal. As provided in more detail below, the clock rolling ofthe metal provides a unique way to achieve a dramatic reduction intexture banding and further provides small and uniform grain sizethroughout the metal surface and thickness. One embodiment of thepresent invention relates to a process for processing or rolling metalcomprising the clock rolling of a metal plate until the desiredthickness is achieved to form a rolled plate. The clock rollinggenerally involves at least two rolling passes and preferably involvesat least three rolling passes, such as from 3 rolling passes to 30 or 40rolling passes or more. Any number of rolling passes within this rangeor above this range can be used depending upon the desired thickness,and uniformity of texture, and/or grain size. With respect to the metal,preferably the metal processed in the present invention is a valve metalor refractory metal or BCC metal but other metals could also be used.Specific examples of the type of metals that can be processed with thepresent invention include, but are not limited to, tantalum, niobium,copper, titanium, gold, silver, cobalt, and alloys thereof.

For purposes of the present invention, clock rolling is where a metalarticle, such as metal plate, is passed through a rolling mill such asshown in FIG. 2. Any conventional rolling mill which is capable ofcausing metal deformation, such as reducing the thickness of the metal,can be used. As shown in FIG. 2, clock rolling involves rolling a pieceof metal, such as a circular disk, through a rolling mill or press andafterwards, the metal disk is rotated a certain number of degrees andthen passed again through the rolling mill, and afterwards, optionally,rotated again a certain number of degrees and passed through the rollingmill again. After each pass, the same or different true strain can beimparted to the metal by the amount of force imparted by the rollingmill. FIG. 2 shows a preferred clock rolling, which involves a 120°shifting of the disk after each pass. Instead of 120° shifting,generally, any degree of shifting which is preferably more than a 90°shift or less than a 90° shift can be used. In other words, the shiftingof the metal article after each pass can be 100° or more, such as 100°to 170°, after each pass. The number of degrees that the target isshifted after each pass can be the same or different. For instance, asshown in FIG. 2, the metal disk is shifted 120° after each pass.Instead, the metal can be shifted 120° after the first pass, and thencan be shifted 100° after the second pass, and optionally, the thirdpass can involve a degree shifting of 120°, 150°, and the like. Asstated, the shifting generally is more than 90° to avoid a meretransverse or cross-directional rolling schedule. Furthermore,preferably, after each rolling pass, the shifting of the article willnot be within 10° of being transverse or cross-directional. Furthermore,the clock rolling can involve turning the metal article upside down andthen subjecting the article to further clock rolling. It is optional torotate the metal a certain number of degrees prior to starting a new setof rolling passes. In other words, and with reference to FIG. 2, if a120° clock rolling is used, after 3 passes, instead of rolling at thesame starting point designated as 1 with the next rolling, the metal canbe rotated any number of degrees, such as 10° to 110°, prior to the nextpass so that the rolling direction is scattered throughout the metaldisk or other article.

In at least one embodiment, no annealing is provided to the work pieceprior to or during the rolling operation. The rolling operations can beconducted at room temperature. During the deformation process, the workpiece temperature can increase in temperatures, e.g., for tantalum—toapproximately 150° C. It is possible to heat the work piece prior torolling to a temperature, for instance, of 40° C. to 350° C. to reducethe force required from the rolling mill. Using a large number ofrolling passes to achieve the desired thickness enhances uniformity ofthe part. True strain per rolling pass typically ranges from about 0.3to about 0.04.

The metal that is subjected to clock rolling can be obtained by forgingor otherwise mechanically deforming a billet to form the metal platethat is subjected to clock rolling.

In one embodiment, the true strain imparted by clock rolling can be fromabout 1.0 to about 2.0, and more preferably, from about 1.2 to about1.9, or any number in between. Furthermore, the true strain imparted byeach single rolling pass can be from about 0.02 to about 0.5. Other truestrain values above or below this range can also be achieved.

As stated, the clock rolling can involve clock rolling on one side ofthe metal plate and then clock rolling on the opposite side of the metalplate. The number of passes of clock rolling on one side and then on theopposite side can be the same or different or can be similar.

The forging of the billet to obtain the metal plate is preferably axialforging. The forging can impart, in at least one embodiment, a truestrain of from about 0.75 to about 2.0. The true strain value can beabove or below this range, as well. The billet that is subjected toforging can have a ratio of billet length to billet diameter of about 3or less. Preferably, the forging imparts a true strain ranging fromabout 0.8 to about 1.4.

The billet can be obtained by extruding or swaging a metal ingot to adesired diameter to form an extruded or swaged ingot. The ingot can becommercially available. The ingot can be prepared in accordance with theteachings of Michaluk et al., U.S. Pat. No. 6,348,113, incorporatedherein by reference. The method may also include directly casting thehigh purity tantalum metal into a form suitable for deformationprocessing or can form the slab by electron beam melting. The extrudedor swaged ingot can optionally be cut into any size billet for furtherprocessing, such as forging, as described above. The swaged or extrudedingot is next cut into billets with a volume so that the required platevolume can be produced. For example, if a metal plate with a thicknessof 0.5 inch and diameter of 10 inch is desired, then a 4-inch diameterbillet with a length of slightly larger than 3.12 inches can be used.The billet cutting may be conducted by any conventional technique, suchas water-jet cutting, EDM, sawing, or turning on a lathe. The method ofcutting the billet is not particularly critical to the process, providedthat the surface finish on the billet is sufficient to prevent surfacedefects from propagating during the subsequent forming operations. Themetal ingot can have any starting diameter, and preferably has astarting diameter of about 7 inches or more, such as from about 7 inchesto about 13 inches or more. After extruding or swaging, the extruded orswaged ingot, such as billet, can have a diameter of from about 3 inchesto about 7 inches, and more preferably, from about 3 inches to about 6inches (e.g., 4, 5, or 6 inch diameter). Other ingot starting diameterranges can be from 10 inches to 12 inches, from 8 inches to 10 inches,and 6 inches to 8 inches. When the starting ingot is extruded or swaged,in at least one embodiment, the true strain imparted by this extrudingor swaging is from about 0.5 to about 2.0 (e.g., 0.77 to 1.58). Otheringot and billet sizes can be used. The grain size and crystallographicorientation uniformity of the disks tends to be enhanced by using ingotsof 11 inch diameter and is the preferred method for producing sputteringtargets. The swaging or extrusion operation is not required if thestarting ingot diameter is on the order 3 to 6 inches in diameter. Thisswaging or extrusion can be performed at room temperature (10° to 35°C.). It is also possible to perform the swaging or extrusion operationat elevated temperatures such as above 35° C., like 40° C. to 350° C.

It is possible to process the part without annealing after the swagingor extrusion operation. However, if no anneal is provided after swagingor extrusion, the uniformity of the grain structure and orientation isnot as uniform as it is if the billet is annealed after swaging andbefore forging and rolling.

The billet of the proper volume is next forged along the billet axisusing a press. Press forces of around 5000 tons are typically used forpressing billets of tantalum with diameters of 4 to 6 inches. The billetpressing operation is typically conducted at room temperature. However,it is possible to conduct the billet pressing operation with tantalumbillets at elevated temperatures, like 40° C. to 350° C. Thepress-forged billet can be annealed or annealing can be skipped.

The press-forged billet is inspected. If surface defects are found, theyshould be removed by grinding or machining. In addition, improvedquality of the finished part is usually achieved if the billet is groundto have beveled edges to assist with the rolling operation. However,grinding to remove defects and beveling the edges is not required toproduce an acceptable product. The true strain during the press forgingcan, for instance, range from 0.94 to 1.38.

The press-forged billet can be deformed from the forged billet height tothe final plate thickness by rolling. In one preferred embodiment, therolling is conducted by rotating the work piece after each rolling passby 120 degrees. After three passes the work piece may be flipped androlled with another set of three rolling passes with 120 degree rotationof the work piece after each rolling pass. The angle between the firstthree pass set and the second three pass set is offset by 30 degrees.FIG. 2 shows the relationship between the first and second set ofrolling passes. This process is repeated until the thickness of theplate equals the desired value. This rolling process is not orthogonalin order to activate all grains in the metal and reduce the propensityto form texture bands. FIG. 8 shows the difference that the 120 degreeclock rolling makes in the level of texture banding in the rolledtantalum plates. No evidence of texture banding is found in the plateproduced using 120 degree clock rolling, while the plate produced withorthogonal rolling process has a very high degree of texture banding asdetected by the ultrasonic scanning technique.

Optionally, before and/or after any step in any of the processesdescribed herein, one or more annealing steps can occur. In oneembodiment, the rolled plate can be annealed (after clock rolling) andpreferably no earlier annealing occurs beforehand throughout the entireprocess. In other words, there is no annealing of the ingot, the billet,or the forged billet into a plate.

As an option, after extruding or swaging the ingot, the extruded orswaged ingot can also be annealed. The grain size and crystallographicorientation uniformity of the disks tends to be enhanced by annealingthe material after swaging or extruding and after rolling. However,acceptable grain size and crystallographic texture uniformity can alsobe achieved by annealing only after rolling.

If annealing is used after swaging, the anneal can occur before or aftercutting the swaged ingot into billets. The choice will depend upon thecapability of the annealing furnace to accept long swaged ingot orsmaller cut billets.

With respect to annealing of the tantalum, preferably this annealing isin a vacuum annealing at a temperature and for a time sufficient toachieve complete recrystallization of the tantalum metal. As indicatedabove, the tantalum ingot and any form of the ingot formed afterwardscan be annealed one or more times before and/or after any step mentionedherein. The annealing can be at any conventional annealing temperature,such as a temperature that causes at least partial recrystallizationand/or alteration in grain size.

The annealing can occur at any suitable temperature. For instance, theannealing can be conducted in a vacuum at a temperature of from about975° C. to about 1125° C. Other temperatures can be used. A heating rateof 10° to 50° C./min. (e.g., 30° C./min.) can be used. The grain sizeand crystallographic orientation uniformity of the disks tends to beenhanced by annealing the billets after forging and this is thepreferred method for producing sputtering targets. However, in somecases this additional anneal is not required to meet the productrequirements. In these cases, the intermediate anneal may be skipped.

The metal from the combined forging and rolling steps can have a truestrain imparted by the steps that ranges from about 2 to about 3.5.However, other true strain values above and below this range can also beachieved.

In the process of the present invention, and in at least one embodiment,a true strain reduction of at least 3.0, at least 4.0, or, for instance,from about 3.0 to about 6.0, is imparted to the rolled plate during theentire process.

In another embodiment of the present invention, the present inventionrelates to a process for making a circular metal article which comprisesprocessing a metal ingot having a cylindrical shape so that thecylindrical shape is maintained throughout the entire process. Putanother way, the circular shape of the starting material maintains itscircular shape throughout all the processing including extruding orswaging, forging, rolling, and any other processing of the metal,whether it is polishing, thermal mechanical working of the metal, andthe like.

In the present invention, in one embodiment, by using a process ofswaging, extrusion, rotary forging, and upset forging withoutlubrication in combination with clock rolling, circular metal targetdisks with very strong (111) crystallographic textures can be made.Instead of strong (111) textures, very strong (100) or othercrystallographic textures can be obtained.

In one mode of the present invention, annealing does not interrupt themetal deformation and consequently, a higher true strain is inputted tothe metal prior to annealing. For instance, tantalum with true strainsof 4.43 or more have been achieved without annealing. The metal ispreferably only annealed after all mechanical deformation is completedand only annealed once or twice during the target formation process.Annealing is an expensive process generally requiring that the metal beprotected from oxygen and nitrogen by either a vacuum, argon atmosphereor by coating the metal in a protective layer that prevents oxygen andnitrogen diffusion into the metal. This is especially true for tantalumor niobium. Oxygen and nitrogen in tantalum are known to adverselyaffect the tantalum mechanical properties making tantalum less ductile.Consequently, by eliminating annealing steps in the manufacturingprocess, the quality of the metal is improved (e.g., less oxygen andnitrogen contamination) and the cost for producing the sputtering targetis reduced.

In the present invention, the cylindrical ingot is processed so that thecircular shape is maintained throughout the process. The material yieldof the process is improved by a factor of at least two by maintainingcircular shape.

In the present invention, the tantalum metal or other bcc metal, canhave any purity such as 95% or greater. Preferably, the purity of themetal is 99% or greater, 99.95% or greater, 99.99% or greater, and99.995% or greater. This purity can exclude gases. Preferably, thetantalum metal or other bcc metal has a purity of at least 99.999% andcan range in purity from about 99.995% to about 99.999% or more. Otherranges include about 99.998% to about 99.999% and from about 99.999% toabout 99.9992% and from about 99.999% to about 99.9995%. The presentinvention further relates to a metal alloy which comprises the bcc metalor tantalum metal, such as a tantalum based alloy or other alloy whichcontains the bcc metal or tantalum as one of the components of thealloy. While the description at times involves the preferred metal,tantalum, it is to be understood that the entire description throughoutthis application equally applies to other valve metal or bcc metals.

The impurities (e.g., metallic impurities) that may be present in thetantalum metal can be less than or equal to 0.005% and typicallycomprise other bcc refractory metals of infinite solubility in tantalum,such as niobium, molybdenum, and tungsten. For instance, metallicimpurities, like Mo, W, and Nb (in the case of Ta) can be below(individually or combined) 100ppm, below 50 ppm, below 20 ppm, below 10ppm, or even below 5 ppm total. The oxygen content can be below 100 ppm,below 50 ppm, below 20 ppm, or below 10 ppm. All other elementalimpurities, (including radioactive elements) whether metal or non-metalcan be below a combined amount of 200 ppm, below 50 ppm, below 25 ppm,or below 10 ppm or even lower and optionally having 50 ppm or less O₂,25 ppm or less N₂, or 25 ppm or less carbon, or combinations thereof.

The tantalum metal and alloys thereof containing the tantalum metalpreferably have a texture which is advantageous for particular end uses,such as sputtering. As an option, in each of the embodiments describedthroughout the present invention, the texture can be uniform on thesurface and/or throughout the thickness of the metal. Preferably, whenthe tantalum metal or alloy thereof is formed into a sputtering targethaving a surface and then sputtered, the texture of the tantalum metalin the present invention leads to a sputtering target which is easilysputtered and, very few if any areas in the sputtering target resistsputtering. Further, with the texture of the tantalum metal of thepresent invention, the sputtering of the sputtering target leads to avery uniform sputtering erosion thus leading to a sputtered film whichis therefore uniform as well. A texture capable of resulting in asputtering target which is easily sputtered can be a mixture of texturesthat are uniformly distributed in the tantalum metal.

It is preferred that the tantalum metal have a fine texture. In oneembodiment, the texture is such that the (100) peak intensity within any5% incremental thickness of the tantalum is less than about 15 random,and/or has a natural log (Ln) ratio of (111):(100) center peakintensities within the same increment greater than about −4.0 (i.e.,meaning, −4.0, −3.0, −2.0, −1.5, −1.0 and so on) or has both the (100)centroid intensity and the ratio above. The center peak intensity ispreferably from about 0 random to about 10 random, and more preferablyis from about 0 random to about 5 random. Other (100) centroid intensityranges include, but are not limited to, from about 1 random to about 10random and from about 1 random to about 5 random. Further, the log ratioof (111):(100) center peak intensities is from about −4.0 to about 15and more preferably from about −1.5 to about 7.0. Other suitable rangesof log ratios, include, but are not limited to, about −4.0 to about 10,and from about −3.0 to about 5.0. Most preferably, the tantalum metal ofthe present invention includes a grain size and preferred texture withregard to the (100) incremental intensity and the (111):(100) ratio ofincremental centroid intensities. The method and equipment that can beused to characterize the texture are described in Adams et al.,Materials Science Forum, Vol. 157-162 (1994), pp. 31-42; Adams et al.,Metallurgical Transactions A, Vol 24A, April 1993-No. 4, pp.819-831;Wright et al., International Academic Publishers, 137 Chaonei Dajie,Beijing, 1996 (“Textures of Material: Proceedings of the EleventhInternational Conference on Textures of Materials); Wright, Journal ofComputer-Assisted Microscopy, Vol. 5, No. 3 (1993), all incorporated intheir entirety by reference herein. In one embodiment, the tantalummetal has a) an average grain size of about 50 microns or less, b) atexture in which a (100) pole figure, has a center peak intensity lessthan about 15 random or c) a log ratio of (111):(100) center peakintensities of greater than about −4.0, or a combination thereof.

For purposes of the present invention, the texture can also be a mixedtexture such as a (111):(100) mixed texture and this mixed texture ispreferably uniform throughout the surface and/or thickness of the plateor target. In another embodiment, the tantalum preferably has a primaryor mixed (111) texture, and a minimum (100) texture throughout thethickness of the sputtering target, and is preferably sufficiently voidof (100) textural bands.

Furthermore, with respect to the texture of the ingot, plate, orfinished plate or target, the texture can be any texture such as aprimary (100) or primary (111) texture or a mixed (111):(100) texture onthe surface and/or throughout the thickness of the material, such as theslab. Preferably, the material, such as the slab, does not have anytextural banding, such as (100) textural banding when the texture is aprimary (111) or mixed (111):(100) texture.

The grain size of the tantalum metal can also affect the uniformity ofthe sputtering erosion and the ease of sputtering. The tantalum metal ofthe present invention can have any grain size. Preferably, the tantalummetal of the present invention includes an average grain size of about1,000 microns or less, 750 microns or less, 500 microns or less, 250microns or less, 150 microns or less, 100 microns or less, 75 microns orless, 50 microns or less, 35 microns or less, 25 microns or less, 20microns or less, 15 microns or less, or 10 microns or less. Other grainsizes that are suitable in the tantalum metal of the present inventionare grain sizes having an average grain size of from about 5 to about125 microns. Preferably, the tantalum metal of the present inventionincludes an average grain size of from about 10 to about 100 microns.The tantalum metal of the present invention can include an average grainsize of from about 5 to about 75 microns or from 25 to 75 microns, orfrom about 25 to about 50 microns. Also, in one embodiment, 95% of thegrain sizes are 100 microns or less. This can be determined by measuring500 grain sizes on a sample. Preferably, 95% of the grain sizes are 75microns or less. Also, 95% of the grains can be less than 3 times theaverage grain size.

In one embodiment of the present invention, the product resulting fromthe process of the present invention preferably results in plates orsputter targets wherein at least 95% of all grains present are 100microns or less, or 75 microns or less, or 50 microns or less, or 35microns or less, or 25 microns or less. More preferably, the productresulting from the process of the present invention results in plates orsputter targets wherein at least 99% of all grains present are 100microns or less or 75 microns or less or 50 microns or less and morepreferably 35 microns or less and even more preferably 25 microns orless. Preferably, at least 99.5% of all grains present have this desiredgrain structure and more preferably at least 99.9% of all grains presenthave this grain structure, that is 100 microns or less, 75 microns orless, 50 microns or less and more preferably 35 microns or less and evenmore preferably 25 microns or less. The determination of this highpercentage of low grain size is preferably based on measuring 500 grainsrandomly chosen on a microphotograph showing the grain structure.

In at least one embodiment, the plate (as well as the sputter target)can be produced wherein the product is substantially free of marbleizingon the surface of the plate or target. The substantially free ofmarbleizing preferably means that 25% or less of the surface area of thesurface of the plate or target does not have marbleizing, and morepreferably 20% or less, 15% or less, 10% or less, 5% or less, 3% orless, or 1% or less of the surface area of the surface of the plate ortarget does not have marbleizing. Typically, the marbleizing is a patchor large banding area which contains texture that is different from theprimary texture. For instance, when a primary (111) texture is present,the marbleizing in the form of a patch or large banding area can be a(100) texture area which is on the surface of the plate or target andmay as well run throughout the thickness of the plate or target. In oneembodiment, this patch or large banding area can generally be considereda patch having a surface area of about 0.25% or more of the entiresurface area of the plate or target and may be even larger in surfacearea such as 0.5% or 1%, 2%, 3%, 4%, or 5% or higher with respect to asingle patch on the surface of the plate or target. There may certainlybe more than one patch that defines the marbleizing on the surface ofthe plate or target. The present invention serves to reduce the size ofthe individual patches showing marbleizing and/or reduces the number ofoverall patches of marbleizing occurring. Thus, the present inventionminimizes the surface area that is affected by marbleizing and reducesthe number of marbleizing patches that occur. By reducing themarbleizing on the surface of the plate or target, the plate or targetdoes not need to be subjected to further working of the plate or targetand/or further annealing. In addition, the top surface of the plate ortarget does not need to be removed in order to remove the marbleizingeffect.

Using the non-destructive banding test referred to above in U.S. patentapplication Ser. No. 60/545,617 (incorporated in its entirety byreference herein), the present application can confirm very low bandingquantitatively in various embodiments of the present invention. Thus, inat least one embodiment, the present invention also relates to metalarticles, such as metal plate, that have a very low amount of texturalbanding area in the metal. This percentage of textural banding area canbe determined by the automatic ultrasonic detecting method described inU.S. patent application Ser. No. 60/545,617 or by other means. In moredetail, based on the measurement data achieved by a detecting method, apercentage of banding in a portion or overall area of the metal articlecan be readily determined. As part of the present invention, the presentinvention relates to metal articles having a total percent banding areaof less than 1% (based on the overall area scanned for detection). Thepercent of the banding area can be with respect to the percent bandingarea only within the thickness of the metal article. Thus, in at leastone embodiment, the percent banding area excludes surface texturalbanding which is visible before or after the surface is etched. One wayto determine the percent banding area, in the case of an ultrasonicdetecting method, can be based on the number of pixels which meet athreshold level which correspond to textural banding. Put another way,the ultrasonic detecting method can be calibrated with a known objecthaving banding, and thus, a threshold number can be obtained which wouldclearly indicate banding or correlate to banding. After this calibrationis achieved, the metal article to be tested can then be subjected to theultrasonic detection and the number of pixels meeting a thresholdnumber, e.g., signal intensity, would be considered corresponding to abanding area. Upon the particular metal article or portion thereof beingmeasured, the number of pixels meeting the pre-determined thresholdwould then be considered a detection of a texture banded area and thenumber of pixels having this banded area can then be compared to theoverall number of pixels to determine the percent banding area. Theamount of resolution used by the ultrasonic detecting method can be anyresolution and, certainly, the higher the resolution, the more precisethe percent banding area can be determined. For instance, the resolutioncan be 5 mm or less, and more preferably 1 mm or less. A resolution thatworks well is from about 0.5 mm to 1.5 mm with respect to the pixelresolution. The texture banding area percentages are all below 1%, e.g.,from 0.10 or lower to 0.95%, and preferably from about 0.10 to 0.50% orless than 0.50%, or from 0.10 to 0.45%, or 0.10 to 0.25% or 0.1 to 0.4%.The present invention permits the lowest texture banding seen by theinventors thus far. While some of the previous methods by CabotCorporation have made metals with low texture banding on the order of0.6 or 0.7% or higher, the present invention has unexpectedly obtainedmetals with texture banding below 0.6% on a routine basis.

In at least one embodiment of the present invention, the presentinvention obtains an axial texture for the metal articles such as metalplates or targets. Preferably, the axial texture is a symmetrical axialtexture. For instance, the axial texture of the metal article can have,as a primary axis, <111> or can have, as a primary axis, <100>. Someskilled in the art will use the term “predominant” texture or “strong”texture to characterize crystallographic texture with the primary axisof <111> or with the primary of <100>. For instance, as shown in FIG. 3of the present application, an example of an axial texture for tantalumplate, which happens to be a sputtering target, is shown. FIG. 3 showsstrong axial primary crystallographic texture of <111>. U.S. Pat. No.6,348,113 B1 provides a description of “texture” and related terms. The<110> and <100> poles are randomly distributed and/or have a symmetricalaxial texture as a result of a rotation about the <111> axis as shown inFIG. 3. For purposes of the present invention, the present inventionfurther relates to metal articles such as metal plates or sputtertargets, such as BCC metal articles (e.g., BCC metal plates or BCC metalsputter targets, such as tantalum, niobium, or alloys thereof) that havean axial texture where, in the axial texture, the primary axis is<111 >or <100>. As can be seen by comparing FIG. 3 with FIG. 9, whereinFIG. 9 represents a tantalum plate made by conventional thermomechanical orthogonal rolling, the <110> and <100> pole distributionsare not random and/or are unsymmetrical and are more directional withrespect to its orientation relative to the primary (111)crystallographic texture. This stronger orientation in certaindirections leads to less uniform sputtering of the target. Accordingly,in one embodiment of the present invention, the present inventionrelates to a metal article that has the pole figures of FIG. 3 where itis understood that the primary axis can be <111> or <100>. While FIG. 3shows a primary (111) crystallographic texture, is to be understood thata similar pole figure can be achieved where the axis is a primary (100)crystallographic texture. This axial texture is especially importantwith rolled plate such as BCC metal rolled plate or BCC metal sputtertargets. In addition, the present invention permits one to obtain a verystrong axial primary (111) crystallographic texture or a very strongaxial primary (100) crystallographic texture wherein the non-primarycrystallographic texture is very weak in the axis.

Preferably, the metal is at least partially recrystallized, and morepreferably at least about 80% of the tantalum metal is recrystallizedand even more preferably at least about 98% of the tantalum metal isrecrystallized. Most preferably, the tantalum metal is fullyrecrystallized. For instance, the tantalum product preferably exhibits auniform texture of mixed or primary (111) on the surface, throughout itsthickness, or a combination thereof as measured by electron backscatterdiffraction (EBSD), such as TSL's Orientation Imaging Microscopy (OIM)or other acceptable means. The resulting tantalum can include anexcellent fine grain size and/or a uniform distribution. The tantalumpreferably has an average recrystallized grain size of about 150 micronsor less, more preferably about 100 microns or less, and even morepreferably about 50 microns or less. Ranges of suitable average grainsizes include from about 5 to about 150 microns; from about 30 to about125 microns, and from about 30 to about 100 microns.

Preferably, the sputtering targets made from the tantalum of the presentinvention have the following dimensions: a thickness of from about 0.080to about 1.50″, and a surface area from about 7.0 to about 1225 squareinches. Other dimensions can be made.

The definition of true strain is e=Ln(ti/tf), where e is the true strainor true strain reduction, ti is the initial thickness of the plate, tfis the final thickness of the plate, and Ln is the natural log of theratio.

The metal plate of the present invention can have a surface area thathas less than 75%, such as less than 50% or less than 25%, of lusterousblotches after sputter or chemical erosion. Preferably, the surface areahas less than 10% of lusterous blotches after sputter or chemicalerosion. More preferably, the surface area has less than 5% of lusterousblotches, and most preferably, less than 1% of lusterous blotches aftersputter or chemical reacting.

The various uses including formation of thin films, capacitor cans,capacitors, and the like as described in U.S. Pat. No. 6,348,113 can beachieved here and to avoid repeating, these uses and like areincorporated herein. Also, the uses, metal articles, shapes ,targetcomponents, the grain sizes, texture, purity that are set forth in U.S.Pat. No. 6,348,113 can be used herein for the metals herein and areincorporated herein in their entirety.

The metal plate of the present invention can have an overall change inpole orientation (Ω). The overall change in pole orientation can bemeasured through the thickness of the plate in accordance with U.S. Pat.No. 6,462,339. The method of measuring the overall change in poleorientation can be the same as a method for quantifying the texturehomogeneity of a polycrystalline material. The method can includeselecting a reference pole orientation, scanning in increments across-section of the material or portion thereof having a thickness withscanning orientation image microscopy to obtain actual pole orientationsof a multiplicity of grains in increments throughout the thickness,determining orientation differences between the reference poleorientation and actual pole orientations of a multiplicity of grains inthe material or portion thereof, assigning a value of misorientationfrom the references pole orientation at each grain measured throughoutthe thickness, and determining an average misorientation of eachmeasured increment throughout the thickness; and obtaining texturebanding by determining a second derivative of the average misorientationof each measured increment through the thickness. Using the methoddescribed above, the overall change in pole orientation of the metalplate of the present invention measured through the thickness of theplate can be less than about 50/mm. Preferably, the overall change inpole orientation measured through the thickness of the plate of thepresent invention, in accordance to U.S. Pat. No. 6,462,339 is less thanabout 25/mm, more preferably, less than about 10/mm, and, mostpreferably, less than about 5/mm.

The metal plate of the present invention, can have a scalar severity oftexture inflection (Λ) measured through the thickness of the plate inaccordance with U.S. Pat. No. 6,462,339. The method can includeselecting a reference pole orientation, scanning in increments across-section of the material or portion thereof having a thickness withscanning orientation image microscopy to obtain actual pole orientationsof a multiplicity of grains in increments throughout the thickness,determining orientation differences between the reference poleorientation and actual pole orientations of a multiplicity of grains inthe material or portion thereof, assigning a value of misorientationfrom the references pole orientation at each grain measured throughoutsaid thickness, and determining an average misorientation of eachmeasured increment throughout the thickness; and determining texturebanding by determining a second derivative of the average misorientationof each measured increment through the thickness. The scalar severity oftexture inflection of the metal plate of the present invention measuredthrough the thickness of the plate can be less than about 5/mm.Preferably, the scalar severity of texture inflection measured throughthe thickness of the plate in accordance with U.S. Pat. No. 6,462,339 isless than about 4/mm, more preferably, less than about 2/mm, and, mostpreferably, less than about 9/mm.

The tantalum metal or other metal of the present invention can be usedin a number of areas. For instance, the metal can be made into asputtering target or into chemical energy (CE) munition warhead linerwhich comprises the metal. The metal can also be used and formed into acapacitor anode or into a resistive film layer. The tantalum metal ofthe present invention can be used in any article or component whichconventional tantalum or niobium or other bcc metal is used and themethods and means of making the various articles or componentscontaining the conventional tantalum can be used equally here inincorporating the high purity tantalum metal into the various articlesor components. For instance, the subsequent processing used in makingsputtering targets, such as the backing plate, described in U.S. Pat.Nos. 5,753,090, 5,687,600, and 5,522,535 can be used here and thesepatents are incorporated in their entirety by reference herein.

In the sputter application field, typically a sputtering target assemblyhas a sputtering target and a backing plate. For instance, a metaltarget or metal target blank (e.g., tantalum, titanium, aluminum,copper, cobalt, tungsten, etc.) is bonded onto a backing plate, such asa backing plate flange assembly such as copper, aluminum, or alloysthereof. To achieve good thermal and electrical contact between thetarget and the backing plate, these members are commonly attached toeach other by means of explosion bonding, friction welding, frictionbrazing, soldering, brazing, diffusion bonding, clamping, and by epoxycement and the like.

Examples of the backing plate include, but are not limited to, copper,or a copper alloy, tantalum, niobium, cobalt, titanium, aluminum, andalloys thereof, such as TaW, NbW, TaZr, NbZr, TaNb, NbTa, TaTi, NbTi,TaMo, NbMo, and the like. No limitation exists as to the type ofmaterials used in the sputtering target and the backing plate. Thethicknesses of the backing and the target material can be any suitablethickness used for forming sputtering targets. Alternatively, thebacking plate and the target material or other metal plate to be bondedonto the backing plate can be any suitable thickness for the desiredapplication. Examples of suitable thicknesses of the backing plate andof the target material include, but are not limited to, a backing platewith a thickness of from about 0.25 or less to about 2 inches or more inthickness and targets with a thickness ranging from about 0.060 inchesto about 1 inch or greater. In the present invention, the targetmaterial to be bonded onto the backing plate can be conventional targetgrade material for instance as described in U.S. Pat. No. 6,348,113,incorporated in its entirety by reference herein. The sputtering targetcan also have an interlayer as is conventional in the industry.Furthermore, the sputtering target can be a hollow cathode magnetronsputtering target and can be other forms of sputtering targets such asplanar magnetron assemblies incorporating stationary or rotatingpermanent or electromagnets. The purity, texture, and/or grain size andother parameters, including size and the like are not critical to thepresent invention. The present invention provides a method of making asputtering target assembly with any type of sputtering target andbacking plate.

In at least one embodiment, the target member used to practice thepresent invention includes two sides, a sputtering side and a bondingside which is opposed to the sputtering side. The backing member of thepresent invention includes two sides, a bonding side and a back sidewhich is opposed to the bonding side. The sputtering target assembly ofthe present invention is formed or assembled by fixing the bonding sideof the target member to the bonding side of the backing member. Aninterface is defined by an area between the bonding side of the targetmember and the bonding side of the backing member. The bonding sides canbe fixed to each other such that a surface of the bonding side of thebacking member and a surface of the bonding side of the target memberare in substantial contact; the surfaces of the bonding sides are not insubstantial contact; or, an interlayer can be interposed between aportion of the surfaces of the bonding sides. The interlayer can be abonding media. The interlayer can also be in the form of a foil, plate,or block. Examples of interlayer materials can include, but are notlimited to zirconium and the like and are conventional in the industry,titanium as found in U.S. Pat. No. 5,863,398 and U.S. Pat. No.6,071,389; copper, aluminum, silver, nickel, and alloys thereof, asfound in U.S. Pat. No. 5,693,203, and graphite as found in U.S. Pat. No.6,183,613 B1, each of which is incorporated in its entirety by referenceherein.

The present invention will be further clarified by the followingexamples, which are intended to be exemplary of the present invention.

EXAMPLES

Several different products have been produced using the process of thepresent invention. The following examples are provided to illustrate howthe product is produced.

Product A was produced by first swaging an 11 inch diameter tantalumingot to a 5 inch diameter and then annealing the swaged ingot at 1050°C. for 2 hours. The annealed swaged ingot was then cut into a billet(3.24 inches tall). This billet was forged to a height of 1.26 inches.The forged billet was clock rolled using 9 to 27 passes in order toobtain a finish thickness of 0.36 inches. The rolled plate was annealedat 1050 C for 2 hours. Target disks produced in this way have a truestrain prior to the final anneal of approximately 2.19 and have anaverage grain size of 30 μm and approximately 77% of their (111) planesaligned parallel to the plate surface. Disks produced in this examplehave a diameter of 15 inches.

An alternative method for producing product A is to not anneal after theswaging operation. In this case, the total true strain in the part priorto the final anneal is 2.98 and the average grain size is 30 μm with 77%of their (111) planes aligned parallel to the plate surface.

In another example, Product B was produced by swaging an 11 inchdiameter Ta ingot to 5 inches in diameter, cutting into billets (5.29inches in length) and then annealing at 1050° C. for two hours. Theannealed billets were forged to a height of 2 inches and clock rolled toobtain a finish thickness of 0.55 inches. After rolling, the disks wereannealed at 1050° C. for two hours and then trimmed to produce a finaldiameter of 15.5 inches. In this case, the part had a true strain of2.26 prior to the final anneal. After annealing, this part had anaverage grain size of 63 μm with 61% of its grains with their (111)planes aligned parallel to the plate surface.

In yet another example, Product C was produced by swaging an 8-inchdiameter ingot to 5 inches in diameter, cutting into billets (5.76inches in length) and then annealing at 1050° C. for two hours. Theannealed billets were then forged to a height of 1.75 inches and clockrolled to obtain a finish thickness of 0.36 inches. After rolling, thedisks were annealed at 1050° C. for two hours and then trimmed toproduce a final diameter of 20 inches. In this case, the part had a truestrain of 2.77 prior to the final anneal. After annealing, this part hadan average grain size of 50 μm with 75% of its grains with their <111>direction aligned parallel (within 10 degrees) to the plate surfacenormal.

In another example, Product D was produced by swaging an 11-inchdiameter ingot to 6 inches in diameter, cutting into billets 6.4 inchesin length and then forging to a height of 1.94 inches. The forged billetwas clock rolled to a final thickness of 0.4 inch in 9 to 27 passesrotated 120 degrees between each rolling pass. The clock rolled platewas vacuum annealed at 1050° C. for two hours and then a disk with adiameter of 24 inches was cut from the disk. In this case, the part hada true strain of 3.03 prior to the final anneal. After annealing, thispart had an average grain size of 34 μm with 95% of its grains withtheir <111> direction aligned parallel to the plate surface normal.

This Product (D) may also be produced by swaging an 11-inch diameteringot to 5 inches in diameter, cutting into billets 9.22 inches inlength and then annealing at 1050° C. for two hours. The part isprotected from air during annealing by using a vacuum or by coating thebillet with a protective coating of glass or other oxidation resistantcoating. After annealing, the billet is forged to a height of 2.39inches, clock rolled to a finish thickness of 0.4 inches using 9 to 27rolling passes. The clock rolled plate is annealed at 1050° C. for twohours. Prior to annealing, the part had a true strain of 2.42 and, afterannealing, this part had an average grain size of 55 μm with 64% of itsgrains with their (111) planes oriented parallel (within 10 degrees)with the plate surface.

In another example, Product E was produced by swaging an 8-inch diameteringot to 6 inches in diameter, annealing at 1050° C. for one to threehours and then cutting into billets of 10 inches in length. The billetswere forged to a height of 2.51 inches and then clock rolled to a finalthickness of 0.4 inches. The rolled disk was vacuum annealed at between975 and 1125 C for one to three hours. The disks prior to the finalanneal had an unannealed true strain of 3.22 and, after annealing, hadan average grain size of 38 μm with 82% of its grains with their <111>direction aligned parallel to the plate surface normal. This disk can bealso produced without annealing between the swaging step and the forgingstep.

Typically, when conventional tantalum plate is rolled, the tantalummetal grains rotate under the applied stress to produce characteristiccrystallographic orientations in the rolling and transverse directions.Then, when the rolled plate is then formed into a cup or dome shape, theflow of the tantalum during the cup or dome shape formation will varyrelative to the rolling direction of the plate. These variations in flowcharacteristic that arises from differences in the metalcrystallographic orientation cause the cup or dome shaped object to ear,which is undesirable. Earring occurs whenever rolled plate that is notisotropic in the rolling plane is formed into cup shapes. Earringreduces the material efficiency of the process, since additionalmaterial must be added to the plate so that there is enough materialafter earring to produce the finished target. The present inventionreduces or completely eliminates earring since the present inventionprovides a plate or target that deforms isotropically in any directionwithin the disk plate, thus avoiding or reducing the earring problem.

In some sputtering target designs, the metal plate is further shapedinto a more complex shape. Examples of these types of sputtering targetsinclude the designs using a hollow-cathode structure. In this case, spinforming, forging, hydro-pressing, drawing or other methods of formingmetal plate are used to produce a domed or cupped shape with thesputtering plasma contained within the more complex shape. When thesemore complex shapes are required, the metal plate should deformisotropically in any direction within the disk plane. FIG. 7 shows thedifference in earring between tantalum plate using orthogonal rollingprocesses and tantalum plate using the clock rolling process, such as a120-degree clock rolling process. The data in FIG. 7 demonstrates thatthe clock rolling reduces earring by from 0.7 inch to 0.25 inch.

Applicants specifically incorporate the entire contents of all citedreferences in this disclosure. Further, when an amount, concentration,or other value or parameter is given as either a range, preferred range,or a list of upper preferable values and lower preferable values, thisis to be understood as specifically disclosing all ranges formed fromany pair of any upper range limit or preferred value and any lower rangelimit or preferred value, regardless of whether ranges are separatelydisclosed. Where a range of numerical values is recited herein, unlessotherwise stated, the range is intended to include the endpointsthereof, and all integers and fractions within the range. It is notintended that the scope of the invention be limited to the specificvalues recited when defining a range.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the present specification andpractice of the present invention disclosed herein. It is intended thatthe present specification and examples be considered as exemplary onlywith a true scope and spirit of the invention being indicated by thefollowing claims and equivalents thereof.

1. A tantalum metal plate that is circular in shape and having a rollingplane and a thickness of 0.080 to 1.5 inch, wherein said tantalum metalplate is isotropic in said rolling plane and deforms isotropically inany direction within said rolling plane and said tantalum metal platehas a crystallographic texture throughout said thickness wherein saidcrystallographic texture has a pole figure with an axial symmetricaltexture with an axis normal to said rolling plane, wherein said axis hasa primary axial <111> crystallographic texture, with <110> texture and<100> texture poles that are randomly distributed or have a symmetricaltexture around said axis, or said axis has a primary axial <100>crystallographic texture, with <110> texture and <111> texture polesthat are randomly distributed or have a symmetrical texture around saidaxis, and said tantalum metal plate has a percent texture banding areaof less than 0.5% with respect to overall area and volume of saidtantalum metal plate that is inconsistent or non-uniform with respect tothe primary texture present in said tantalum metal plate, and saidtantalum metal plate has a purity of at least 99.99% Ta and an averagegrain size of 150 microns or less.
 2. The tantalum metal plate of claim1 having the pole figures of FIG.
 3. 3. The tantalum metal plate ofclaim 1, wherein said axis is a primary axial <111> crystallographictexture, with <110> texture and <100> texture poles that are randomlydistributed or have a symmetrical texture around said axis.
 4. Thetantalum metal plate of claim 1, wherein said axis is a primary axial<100> crystallographic texture, with <110> texture and <111> texturepoles that are randomly distributed or have a symmetrical texture aroundsaid axis.
 5. The tantalum metal plate of claim 1, wherein said percenttexture banding area is with respect to (100) texture banding.
 6. Thetantalum metal plate of claim 1, wherein said metal article has auniform mixed (111):(100) texture.
 7. The tantalum metal plate of claim1, wherein said tantalum metal plate is a sputter target that is bondedto a backing plate.
 8. The tantalum metal plate of claim 1, whereinpercent banding area is from 0.1 to less than 0.5%.
 9. The tantalummetal plate of claim 1, wherein percent banding area is from 0.1 to0.4%.
 10. The tantalum metal plate of claim 1, wherein said percentbanding area is from 0.1 to 0.25%.
 11. The tantalum metal plate of claim1, wherein said tantalum metal plate is a sputter target disk.
 12. Thetantalum metal plate of claim 11, further comprising a backing plateattached to said sputter target disk.
 13. The tantalum metal plate ofclaim 1, wherein said primary texture is a primary (111) texture. 14.The tantalum metal plate of claim 13, wherein said tantalum metal plateis a sputter target blank.